Apparatus for forming aggregates of powdered materials



OC- 22, 1968 D. F. PoBsT, JR., ETAL 3,406,426

APPARATUS FOR FORMING AGGREGATES OF POWDERED MATERIALS F l G ATTORNEYOct. 22, 1968 Original Filed June 6, 1963 D. F. PoBST, JR., ETAL3,406,426

APPARATUS FOR FORMING AGGREGATES OF POWDERED MATERIALS 4 Sheets-Sheet 2v y 35 d8 P20 CONVERTERv 34 TRANSFORMER 36 \|9 MSNM AIR 4% G4; 11, 4'7PNEUSUIC 3% 39 33 V CONTROLLER ELEcTRo-PREuMAT|c TRANsoucER DRY ORWETTED POWDER wETrlRs 5| 7 LlOulO l I3 5 R 8? 3] ,22 HHIIIIUHHIIIHIHI L.LllIl/U/llulllllllllllllljl]l M (/1 44 I5 I H n I6 3o l 2 POSITIORERQ'?MOTIVATING (14 AIR supp-UTD AOOREGATES INVENTORS D AVI D F. POBST, JR.

ATTORNEY Oct. 22, 1968 n. F. POBST, JR., ETAL. 3,406,426

APPARATUS FOR FORMING AGGREGATES OF POWDERED MATERIALS Original FiledJune 6, 1963 4 Sheets-Sheet 5 my 527 47 (3 52 5H- INVENTORS D AVID FPOBST, JR.

BOBBY J. R LETT 37AM,

ATTORNEY Oct. 22, 1968 D. F. POBST, JR.. ETAI. 3,406,426

AP'ARTUS FOR FORMING AGGREGATES OF POWDERED MATERIALS Orifinal FiledJune 6, 1953 4 Sheets-Sheet 4 v INVENTORS DAVID F.POBST,JR. BOBBY J.

R0 ETT 2%@ 5&1@

ATTORNEY United States Patent APPARATUS FOR FORMING AGGREGATES OFPOWDERED MATERIALS David F.`Pobst, Jr., and Bobby J. Rowletf, Franklin,La., assignors to Columbian Carbon Company, New York, N.Y., acorporation of Delaware Original application June 6, 1963, Ser. No.286,042, now Patent No. 3,304,355, dated Feb. 14, 1967. Divided and thisapplication Oct. 25, 1966, Ser. No. 601,258

v 8 Claims. (Cl. 18-1) ABSTRACT OF THE DISCLOSURE This invention relatesto aggregating or -pelletizing apparatus of the general type in which afinely powdered material is converted into discrete, pasty aggregates byvigorous mechanical agitation of the powder with a liquid pelletizingagent e.g. water. The present invention'is an improvement on priorapparatus since novel means are provided for regulating the amount ofwork transferred into the wetted powdered material during the agitationthereof to form the pasty aggregates.

This is a division of application Ser. No. 286,042, filed June 6, 1963,now U.S. Patent 3,304,355.

The invention is especially useful as applied to the pelleting of carbonblack and will be more fully described Vand illustrated herein withparticular reference to that application. It will be understood,however, that the invention is not so restricted but is applicable tothe aggregating or pelleting of other powdered materials.

In order to effectively utilize some solid -materials n a preferredmanner, it is necessary thaty they be produced as a powder or beconverted to powdered form by subdivision, e.g., by grinding orpulverizing Quite frequently, however, it is desired to convertthe-material, prior to its intended use, from the powdered state to apelleted form in order to enhance its handling properties. Carbon black,for instance, is produced as a light flocculent powder and it has beencustomary to reduce the powder to beads or pellets prior to shipping,storing or use. The advantages of converting such powdered materials topelleted form are Well known to the industry and need not here befurther recited.

, One well-known method for reducing powdered material to aggregate orpelleted form involves the step of vigorously agitating the powderedmaterial, carbon black, for instance, with a wetting liquid, e.g.,water, and, as previously noted, the present invention is directed toimprovements in that type of operation.

Such pelleting operations are affected by many variables whichcomplicate regulation and control of the physical characteristics of thefinished product. If too fragile, the pellets may be damaged byexcessive handling and may be reduced, at least in part, back to thepowdered state. If, on the other hand, the particles comprising thepellets are too tightly bound together, their redispersion may be overlydifficult.

In the pelleting of carbon black, for instance, the wetting liquid usedmay be water, as such, or an aqueous solution or emulsion of a bindingor agglutinating agent, e.g., sugar, a resin or a protein glue, and theresultant pellets are usually dried prior to shipment or storage.

The agitation of the powdered material with the Wetting agent is, withadvantage, effected by known procedure involving the passing of thepowdered material and wetting agent, vin controlled proportions, througha horizontally elongated chamber or conduit in which there is rotatablymounted a coaxially-positioned shaft to which there are afiixed amultiplicity of spaced radially-extending elements, eg., rods. Uponrotation of the shaft, the

3,406,426 Patented Oct. 22, 1968 material pasing longitudinally throughthe chamber is subjected to impact and agitation by the rapidlyrotating, radially projecting, spaced members which cause the particles,while in a continuous mass, to tumble and roll by reason of the actionof the agitating members and to slide off the surfaces of the agitatingmembers, as well understood in the art.

By controlling both the nature of the agitation and the extent to whichthe particles are wetted, discrete pasty aggregates may be formed havinga high order of roundness. After formation, the aggregates may be driedto remove the bulk of the wetting liquid and produce fir-m pellets. Highquality carbon black pellets are characterized by an apparent bulkdensity which is higher than that of the parent powder, are more freelyflowing, and are substantially free of fines or dusts. They are furthercharacterized by a high packing point and optimum crushing strength,these being necessary to prevent compaction or destruction in handling,without the power particles being so thightly bound together as to maketheir redispersion overly difficult.

In aggregating and pelleting carbon blacks, after the manner described,formation of the aggregates is inuenced by several critical variableswhich affect importantI physical characteristics of the aggregates and,consequently, those of the finished pelleted product. The correctvproportion of wetting liquid must be employed before the discreteaggregates will form. An excessive or insufficient quanity of the liquidwill result in mudding out and dusting out, respectively. Also, acorrect amount of work must be performed on the mass in agitating themass of particles to optimize formation of the aggregates.

The term work input or work input value as used herein, denotes the workinvolved in moving the spaced agitating members through the mass ofwetted particles, i.e., energy transferred from the agitating members tothe partly unyielding mass as the said members move through it. The termcritical work input level as used herein is intended to mean a workinput value which must exist to optimize formation of aggregates havinga specific combination of physical characteristics. Excessive work inputis destructive of aggregates already formed while insuflicient workinput will not thoroughly aggregate the wetted powder. A critical workinput level may, therefore, be an optimization of constructive anddestructive values to permit the formation of aggregates having amaximum degree of roundness and uniformity of size, while minimizing theamount of dust or fines which remain after agitation,

Prior to this invention, various methods were utilized for establishinga work input employed in agitating the wetted powder by varying theresistance to movement of the agitating members. None, however, hasprovided means for precisely maintaining the work input valve duringfluctuation of, or after altering, variables such as the flow rate ofthe wetted powder through ythe zone of agitation; the consistency of thewetted particles, e.g., degree of stiffness or pastiness; or the patternof flow of the wetted powder through the zone of agitation.

Previously, work input values have been established by means of astationary weir or orifice, positioned near the ou-tlet of the agitatingzone, for retaining a fixed volume of the wetted powder particles withinthe zone of agitation. The resistance offered to the agitating membersby the retained mass could not, therefore, be altered input level had tobe re-established by manually substituting another size stationary Weiror orifice, which usually required shutting down the aggregatingoperation. Adjustment and regulation of the work input value by manualmeans was for the most part unsatisfactory, and difficult, and providedonly incremental changes which were usually inadequate for optimizingthe formation of the aggregates.

v The diiculties heretofore experienced are avoided by our presentinvention whereby we establish a critical work input level, i.e.,optimal for producing a pelleted material having the desired properties,and once established, maintain this optimal work input level, withoutinterruption of the operation, and in spite of changes and liuctuationsin other operating conditions, all as hereinafter as more fullydescribed and illustrated.

The invention will be further described and illustrated .wtih referenceto the accompanying drawings, which represent specic embodimentsthereof, but it will be understood that the invention is not limitedthereto, since other embodiments of the invention will be apparent fromthis description.

FIGURE l of the drawings is a somewhat diagrammatic owsheet illustratinghow the invention may, with advantage, be applied to a process formaking dried pellets of powdered materials.

FIGURE 2 is another somewhat diagrammatic flowsheet illustrating controlapparatus which may be employed in forming the aggregates.

FIGURE 3 is a fragmentary vertical side view, partly insection, of anagitating device which may be employed for forming the aggregates.

FIGURE 4 is a similar fragmentary vertical side view of the device ofFIGURE 3 showing in greater detail a conjunctive damper arrangementwhich may be employed for adjusting and regulating the work inputemployed in forming the-aggregates.

FIGURE 5 is a sectional view taken along the line 5 5 of FIGURE 3.

FIGURE 6 is a fragmentary, vertical sectional view of an agitatingdevice similar to that of FIGURE 3 but employing a somewhat differentconjunctive damper arrangement, which may also be employed in accordancewith the invention for adjusting and regulating the work input employedin forming the aggregates.

FIGURE 7 is a sectional view of FIGURE 6- along the line 7-7.

FIGURE 8 is a sectional view of FIGURE 6 along the line 8 8.

Referring to FIGURE l, the powdered material is fed from the powder bin1 at a predetermined and relatively constant rate by a helicoid conveyor2 and passed into an enclosed conduit 3. A series of spaced agitatingmembers 4 are radially affixed to a rotatable shaft 5 mounted axiallywithin the conduit 3. A wetting liquid, supplied under pressure throughline 6, is fed into the conduit 3 through line 7 and a distributor 8 ata predetermined and relatively constant rate. The rates at which thepowder and the wetting liquid are fed to conduit 3 are variable and maybe regulated at will. The power feed rate may be varied by adjustinglthe rotational speed of the helix 9 by means of a variable speed driveunit 10 and pulleys 10a motivated `by an electric motor 11. The rate atwhich the wetting liquid is fed into conduit 3 may be varied by means ofvalve 12.

Within the conduit 3, the shaft 5 is rotated by torque supplied from aspeed reducer 13 and pulleys 13a motivated by an electric motor 14. Uponrotating the shaft, the afixed agitating members 4 move transverselythrough Athe mass consisting of the powder particles and the wettingliquid. The mass advances. axially through the conduit 3 and dischargesfrom an opening 15.

As the mass advances through conduit 3, it is subjected to amultiplicity of impacts by the moving agitating members 4, and the mass,of course, affords a certain resistance to the movement of members 4therethrough. The value of the resistance, i.e., drag, depends, amongother things, upon the consistency and the volume of the mass and mainlydictates the amount of work which must be employed in moving theagitating members through it and, consequently, the work input informing the aggregates.`

In the agitating devices illustrated herein, the wetted particles arecaused to stick together in the form of discrete macroscopic aggregatesby a rolling or -tumbling action imparted to the particles within themass by the motion of the agitating members, as previously explained.Also, as previously described, the work input during formation of theaggregates strongly influences the physical characteristics. of theaggregates, -and finished pellets produced therefrom. A

lAccording to the present invention the work input is adjusted andregulated by varying the resistance offered to the movement of theagitating members by the wetted powder mass which may be nicelyaccomplished by varying the rate at which the mass is discharged fromthe conduit 3. Not only may the work input level be adjusted andregulated in this way, but the critical work input level may beestablished and maintained, i.e., a work input critical to the formationof aggregates having an exceptionally high order of roundness anduniformity of size.

Using the apparatus represented by FIGURE l, the work input Value may beestablished and regulated by means of a positionable obstructing member,such as damper 16, positioned automatically with respect to the opening15 by means of a positioner 17 which responds to Van actuating electricsignal current generated by a transformer 18 coupled with a power lead19 supplying current to the motor 14. By this arrangement, the positionof the damper 16 may be automatically adjusted and regulated by smallincrements, so as nicely to control the rate at which the owing contentsof conduit 3 discharge through .the opening 15, thereby establishing andmaintaining a critical work input level by continuously controlling theextent to which the conduit is lled with the wetted powder particles,the charge rate to the conduit usually being maintained constant.

The power requirement of the motor 14 varies directly with theresistance offered to the moving of the agitatingmembers by the contentsof the conduit 3. As the power requirement of the motor varies, so alsodoes the current load supplied to the motor through power lead 19. Byfeeding the transformer-generated signal through lines 20 to appropriatecontrol circuitry 21, a variable kbut regulated signal may be suppliedby line 22 to the positioner 17 so that the position of the damper isdependent upon the strength of the signal generated by the transformer.The positioner may, for example7 be motivated by a pressurized fluidsupplied through line 23, so that the position of the damper is dictatedby the value of the fluid pressure which, in turn, is proportional tothe value of the actuating signal supplied to the positioner by line2,2.

By suitable arrangement of the control circuitry, the damper 16 may bepositioned lautomatically to elect the greatest reduction of area of theopening 15 when the current load to the motor 14 is low and, conversely,to effect an Vopening of greater size when the current load is higher.Assuming a fixed consistency for the. wetted powder mass within theconduit 3, it can be seen that when the volume occupied by the mass islowest, maximum obstruction will be presented to the opening 15 by thedamper 16, since the resistance to the moving of agitating members 4,and consequently the motor power requirement, is lowest. On the otherhand, increasing the degree of fill within the conduit 3 increases themotor load, and the damper will be caused to open proportionately.

Advantageously, the control circuitry may also comprise means foradjusting the general location of the damper 16 so that automaticvariation in area of the opening may be accomplished within limits whichare less than the total unobstructed area of the opening, e.g., theopening may be maintained partly closed at all times, while the damperis, nonetheless, repositioned automatically to change thecross-sectional .area of the discharge opening. Within practical andfeasible limits, therefore, any desired work input value maybeestablished and maintained for agitating the wetted powder mass. Byautomatic positioning of the damper in response to a signal proportionalto the motor load, the resistance offered the agitating members by thewetted powder mass may be kept at a constant value, regardless offluctuations in ilow rate of the wetted powder, and the work input valuemay be regulated to the critical work input level. It can be seen thatthe damper is, in fact, positioned automatically in response to anactuating signal which is representative of the work input value, andwhere the critical work input value has been established, it isautomatically maintained.

When one conduit and conjunctive agitating means is not sufficient orpractical for forming satisfactory aggregates, two or` more units havingindependent control circuitry, as illustrated within the confines ofdotted lines A, may be used in'conjunction so that one unit dischargesinto another. The time period of agitation may be significantly extendedby this arrangement, and the wetted powder particles may be subjected todifferent values of work input in each unit, thereby improving thecapability of regulating the physical properties of the aggregates. Ifnecessary, additional quantities of a wetting liquid may be added to thepowder through supplemental supply lines and flow control valves as 24and 25, respectively.

After thepasty aggregates have been satisfactorily formed, they may bedried to produce firm pellets.` If the powder and the wetting liquid arethermally stable, the drying may be accomplished by heating within arotating drum such as represented at 26. The `drum may be heated by asurrounding envelope of hot gases, contained within an enclosure 27, byburning a fuel with air at a controlled rate. Expended heating gases maybe exhausted to the atmosphere through stack 28. Vaporized wettingliquid and the pellets may be fed from the drum into a collector ring 29and separated, so that finished pellets are removed through conduit 30,while the vaporized wetting liquid is removed through a stack 31.

In FIGURE 2, there is illustratedcontrol means which may, withadvantage, be employed for automatically positioning the damper used inconjunction with means previously described, like numerals indicatingcorresponding parts. The shaft 5, having aixed agitating members 4, isrotated by torque supplied from the speed reducer 13 through pulleyarrangement 13a motivated by a three phase A C. electric motor 14. Powersupplied to the motor through lead 19 induces an alternating electriccurrent within the transformer 18. The induction-generated A.C. isconveyed by lines to a converter 32, rectified to D C., and is conveyedthereafter to an electro-pneumatic transducer 33 by lines 34. Amilliammeter 35 may be wired in series with lines 34 to permit visualmonitoring of the electric current value.

The electro-pneumatic transducer may be any suitable device adapted toreceive a variable electric current which it in turn converts to aproportionately variable pneumatic pressure. Air, under pressure, issupplied to the electro-pneumatic transducer through a supply line 3 6and a feeder line 37. From the transducer, a pneumatic pressure is fedto a pneumatic controller 38 through line 39 having a surge tank 40installed therein. Air, under pressure, is also supplied to thecontroller through line 41. From the controller, a pneumatic actuatingsignal pressure is transmitted through a two-way valve 42 and line 22 tothe pneumatic positioner 43.

Motivating air pressure is supplied t-o the pneumatic positioner throughline 23 and a pilot valve 44 installed therein, so that the damperpositioner rod 45 is extended from the positioner upon receipt at thepilot valve 44 of an increased pneumatic actuating pressure from thecontroller, and is retracted by the positionerif said pressure isreduced. The degree of extension or retraction of the positioner rod istherefore proportioned to the extent of the change in pressure inducedwithin line 22.

Since the damper 16 is affixed to the positioner rod 45 by a connector46, and arranged to move so that the area of the opening 15 is changedupon repositioning the damper by moving the positioner rod, it can beseen that the cross-sectional area of the opening and the rate at whichthe contents are discharged therefrom are dependent upon the position ofthe damper, and are changed to a degree which is inversely proportionalto the change in value of the signal current generated by thetransformer 18.

A far lgreater motivating air pressurewill usually be required to extendor retract the rod 45 than is existent within line 22. Motivating air,under sufficient pressure may be supplied to the positioner by line 23through pilot valve 44, which supplies the air to the positioner at apressure which is greater but directly proportional to the actuatingsignal pressure in line 22. l

Advantageously, the pneumatic controller 38 may comprise means forvarying the static pressure in line 22 within a set range (proportionalcontrol). Toy additional advantage, the controller may be equipped withmeans for varying the extent of said range (proportional band control),the response rate of the positioner to the actuating signal (ratecontrol), and means, which may be automatic, for resetting the range inwhich the area of outlet 15 is maintained, thus affording compensationfor any change in variables which dictate a new range (reset control).

By means of a proportional control, the critical work input levelrequired to form the desired high qualitylaggregates may beapproachedrby pre-setting the damper tol maintain the area of the outletopening 15 within a range considered suitable for providing a sufficientmass ofthe wetted powder within conduit 3 which affords an optimum workvalue so long as consistency, flow characteristics and flow rates ofthewetted material do not vary significantly. By means of the proportionalband and rate controls, how-I ever, moderate though signicant changes inthe aforementioned variables may be compensated for by an automatic,-minor adjustment of the degree and rate of iill within the conduit 3;and by means of a reset control, substantial' changes in flow andconsistency may be compensated for 4by effecting a substantial change inthe degree of fill within the conduit, by changing the range of openarea maintained at the outlet 15. Advantageously, the latter may beaccomplished, as previously described, by means responsive to variationsin the electric signal produced bythe transformer 18.

Should it be unnecessary or undesirable to employ the pneumaticcontroller 38, the damper 16 may be precisely positioned, automatically-or by manual control means,

while visuallyvmonitoring the milliammeter 35 to deter- ,l

mine if the desirable or critical work input level is being maintained.To deactivate the controller, valve 47 in line 41 is closed and valve 48is opened to supply air from line 36 to a regulating valve 49 whichmaintains a constant but changeable air pressure in line 50. The two-wayvalve `42 is repositioned to establish intercommunication =be tweenlines 50 and 22, and by manualregulation of the valve 49, the positionof the damper 16 may be adjusted and then held in any `desired positionby the constant pressure present in line 22 after regulation of thevalve is finished. Pneumaticpositioners, pil-ot valves, and pneumatiecontrollers having ffeatures as previously described are well known tothose skilledin the arts and need not here be further described. p

In carrying out the operation, the proportion of wetting liquid requiredfor mixture with the powder to form aggregates may be determined bysimple tests within the apparatus used to effect the agitation. If ytoolittle liquid is 7 employed, the powder particles will not besufficiently wetted to assure complete aggregation. If, on the otherhand, too Imuch liquid is used, a sludge or slime will form instead ofaggregates. When aggregating carbon black powders with water or a diluteaqueous solution or emulsion of a binder or agglutinating agent, theproportion of wetting liquid to black may range as high as 2 parts to 1,by weight, but more usually will lbe within the range of about 0.5 to1.0 part per part of the black, -by weight.

It will .be understood, of course, that the invention is not'applicableto the aggregating of powders which are not readily formed intoaggregates by wetting and agitation, nor powders which it is impracticalto wet.

When the agitation is effected in a conduit, such as described, havingan axially mounted rotatable shaft with affixed agitating members, it isadvantageous that the conduit be elongated in order that the inlet locusfor the dry or wetted powder, such as opening 51, be substantiallyremoved frorn the discharge locus, such as opening 15, so that thewetted powder particles are caused to advance axially from inlet tooutlet over a distance which is at least several times the diameter ofthe conduit. The crosssectional configuration of the conduit may be anythat will permit free rotation of the shaft and affixed agitatingmembers, but to particular advantage may be a closed circle or U-shaped.In the latter case, the conduit may be left open at the top, but morepreferably is closed by a lid.

The speedat which the axially mounted shaft is rotated within theconduit is variable, but especially advantageous results may be obtainedwhen the speed is sufficient to spiral the powder mass so that itconforms to the internal periphery of the conduit as the mass advancestoward the outlet locus. When this condition is effected, more turnblingaction may be imparted than when the particles comprising the massremain near the rotating shaft. It is undesirable, however, to userotational speeds which significantly exceed those critical tocentrifugation of the mass, since excessive power lmay be required forturning the shaft, or work input values may be established which areimpractically high.

The cross-sectional area of the conduit which contains the powder massduring aggregation should, of course, be sufiiciently large toaccommodate a desired throughput rate of the wetted powder particleswithout completely filling the conduit. Similarly, the totalunobstructed area of the opening should be sufiiciently large to preventooding of the conduit at the desired throughput rate, for if the conduitis maintained nearly or completely filled during aggregation, little orno control flexibility is afforded for compensating for fluctuatingvariables which may detrimentally affect the work input level.

When prearranged in accordance with the foregoing considerations, workinput values below the critical work input level may be existent at thedesired throughput rate when the cross-sectional area of the dischargeopening is greatest. By the automatic means, however, the damper maythen be positioned to partly obstruct the discharge opening of theconduit and thus establish and maintain the critical work input value.

In determining the critical work input level necessary for anyparticular powder-wetting liquid combination at a desired rate ofthroughput, it is advantageous to monitor the power requirement forrotating the shaft and affixed agitating members. When an electric motoris employed for the purpose, a wattmeter or ammeter may be installed inthe power supply circuit, or when a control circuit as illustrated inFIGURE 2 is employed an indicating 0r recording ammeter may be used todetermine the electric signal current generated by the transformer,since the strength of this signal is directly proportional to the powerrequirement of the motor. By examining the condition of the aggregatesformed by the agitation, it may be determined when the critical workinput level has been established.

Aggregates formed at the critical work input level are characterized bya very high order of roundness and uniformity of particle size, whilethose formed below the critical level are far more irregular in shapeand size. Accordingly, the work input value established in forming theaggregates may be adjusted, by means as described herein, whilemonitoring the power requirement of the driving means for rotating theshaft 5, to determine the critical work input level required foraggregating a wetted powder at a particular consistency and throughput.Thenceforth, the critical work input level may be maintainedautomatically as previously described.

FIGURES 3, 4 and 5 further illustrate apparatus which may be used toadvantage, in accordance with the invention, particularly when impartinga spiraling motion to the mass so that it conforms more or less to theperiphery of the confining conduit while spiraling and advancing axiallytoward the discharge opening 15. The elongated conduit 3, having aU-shaped cross-sectional configuration, comprises a covering lid 52 andend plates 53 having corresponding mounting fianges 54 and 55,respectively, all of which may be suitably constructed of metal.

A rotatable metal shaft 5 is axially mounted within the conduit by meansof bearings and seals 56 affixed to the end plates. For the agitatingmembers, a series of closely interspaced metal rods, having a circularcross section, are affixed to the shaft in a helical pattern and extendradially therefrom. The conduit 3 is provided with a discharge opening15. A discharge conduit 57 is affixed to the conduit 3 and arranged toreceive the mass discharged through the opening 1S. A damper 16,arranged to be moved transversally with respect to the opening, isattached to positioner rod 45 and is thereby moved automatically bypneumatic positioner 43 affixed to the conduit 3 by brackets 58.

The damper is maintained flush against a flattened segment 59 of theconduit wall by means of guides 60 affixed to the conduit around theopening 15. A bearing and seal 61 may serve as a guide and closure meanswhere the positioner rod 45 extends through the wall of the dischargeconduit 57. The pneumatic positioner 43 is equipped with a motivatingair supply line 23 having a pilot valve 44 installed therein. Variablepneumatic air signal pressures, lower than the motivating air pressureim the line 23, are fed to the pilot valve 44, by line 22 to positionthe damper, by variations in the air signal pressure.

In operation, the rotatable shaft 5 is turned about its axis in thedirection of the arrow 62 (FIGURE 5) at a speed which causes the powdermass to centrifuge within the confines of conduit 3, i.e., the mass iscaused to spiral in the direction of the arrow 62 and conforms t0 theinterior wall of the conduit 3. While swirling, the mass advancesaxially through the conduit toward the discharge outlet 15, and therotational speed remains lower than that of the shaft 5, so that theagitating members 4 move transversally through the spiraling mass as itadvances axially.

Location of the outlet opening 15 and associated damper 16 in the wallof conduit 3, as shown in FIGURES 3, 4 and 5, greatly facilitates thedischarge of a spiraling, advancing mass from the conduit, since thedischarge is effected in a direction tangential to the spiraling path ofthe mass.

FIGURES 6, 7 and 8 represent apparatus similar to that described, butillustrate a different damper-discharge outlet arrangement. A stationaryweir 63 is arranged transversely of the conduit 3 to provide a partialobstruction therein to the axially advancing powder mass. A movabledamper 16 is located atop the stationary weir and is swung on a hinge 64aixed to the wall of the conduit 3. The movable damper 16 is alsoarranged transversely of the conduit 3 and is sized to provideessentially complete obstruction of the conduit when aligned with thestationary weir. The `movable damper is positioned with respect tostationary Weir by means of the positioner rod 45 actuated by thepneumatic positioner 43. When the movable damper is disaligned withrespect to the stationary weir, an outlet opening is created above theWeir and the cross-sectional area of this opening is directlyproportional to the extent of the disalignment.

The advancing mass of wetted powder particles are discharged through theoutlet opening above the weir, and passes to the intercommunicatingdischarge conduit 57. The rate at which the advancing mass dischargesfrom conduit 3 is thus automatically controlled and regulated byadjustment of damper 16 responsive to the impulses passed to thepositioner 43.

In connecting the positioner rod 45 to the hinge-swung damper 16 ofFIGURES 6, 7 and 8, a pin 65 extending radially from the positioner rodserves as an axial mounting member for a freely revolving roller 66. Theroller is coupled with the damper by means of a retaining member 67closely fitted to the roller, but permitting the roller to move freelyacross the face of the damper within the confines of said retainer. Thisarrangement allows the positioner rod to swing the damper on the hingewhile the rod extends and retracts along its axis. A seal and bearingarrangement 68 serves as a guide and closure means where the positionerrod extends through an opening in the end plate 53. The pneumaticpositioner 43 may be secured by means of brackets 70 to a rigid member69 affixed to the conduit 3.

Although the invention has been described with reference to variablearea discharge openings located within the conduit which contains theagitating members, it will be understood that such discharge openingsmay be located elsewhere. It may, for example, be located in another,but intercommunicating, conduit such as the discharge conduit 57, forinstance. Furthermore, it is within the scope of this invention toemploy means other than those disclosed for determining the value of thework input employed in moving the agitating members through the wettedpowder mass.

In accordance with this invention, pellets of carbon black have beenproduced which exhibit an exceptionally high order of roundness anduniformity of particle size, and optimum combinations of packing pointand crushing strength which prevent excessive compaction and crumblingduring normal handling, while maintaining dispersibility of theparticles. Such desirable physical characteristics of the pellets areattributable to the aggregation technique of the invention, i.e., theexceptional values of the characteristics are `dependent upon how theaggregation is effected, and are not equated by adjustments insubsequent processing steps, such as the drying operation, for instance.

Carbon black pellets having a high order of roundness and uniformity ofparticle size provide distinct advantages over those which do not. Ithas `been observed that they ilow more freely and are less subject toauto-detritioning during handling. Additionally, any fractionatingoperation necessary for size separation of the pellets is therebygreatly facilitated. This is especially advantageous for, as a generalrule, pellets of carbon black are screened to separate overs and finesfrom a fraction having a specified size range.

The invention has the further advantage that it permits satisfactoryaggregation of carbon black powder while employing lower than normalamounts of the wetting liquid. This provides the advantage of reducinglthe thermal energy requirement for drying the aggregates. Also, anyrequirement of a binder or agglutinating agent may Ibe substantiallyreduced or eliminated.

It will be understood that various changes may be effected in materials,conditions, equipment arrangements, and the like, which have beendescribed herein to illustrate the nature of vthe invention, withoutdeparting from its spirit or scope as expressed in the appended claims.

We claim:

1. Apparatus for forming pasty aggregates of wetted powdered materialcomprising in combination an elongated conduit adapted to contain anadvancing mass of the wetted powdered material, a shaft rotatablymounted axially within the conduit, said shaft having a series ofagitating members aixed thereto which are spaced along the shaft andextend therefrom in the direction of the conduit wall, said agitatingmembers being adapted to move transversally through said advancing massas the shaft is rotated, said members being further adapted to tumbleand roll said wetted powdered material and thus form pasty aggregatesthereof, a charge inlet opening into one end of said conduit and adischarge opening for said mass leading from the other end of theconduit, means for rotating said shaft, means associated with the chargeinlet opening of the conduit for feeding the powdered material into theconduit at a pre-established rate, means for introducing a wettingliquid into the conduit at a pre-established rate, discharge ratecontrol means associated with said discharge opening for altering therate at which the mass of wetted powdered material discharges from theconduit, means for generating and transmitting to the discharge ratecontrol means an actuating signal havin-g a value proportional to thework input for rotating said shaft, said discharge rate control meansbeing automatically and proportionately responsive to said signal,whereby a critical work level for producing a pelleted material havingdesired properties is established and maintained by altering thedischarge rate of the mass of wetted powdered material from said conduitduring the agitation of said mass therein.

2. The apparatus of claim 1 in which the discharge rate control meanscomprises a positionable damper associated with the discharge openingand adapted to alter the area of the opening and a positioner adapted toposition the damper in -response to said actuating signals.

3. The apparatus `of claim 1 in which thedischarge opening is positionedin the peripheryv of the conduit.

`4. The apparatus of claim 2 in which means for generating the signalstransmitted to the positioner comprises means for producing an electriccurrent of `a value proportional to the work input for rotating theshaft.

5. The apparatus of claim 4 also comprising a transducer for convertingthe electric signals to a fluid pressure signal.

6. The apparatus of claim 2 also comprising means for varying the rateat which the positioner responds to the actuating signals. 7

7. The apparatus of claim 2 in which the positioner is operated by uidpressure and the actuating signal transmitted to said positioner is afluctuation in uid pressure.

8. The apparatus of claim 2 in which the positioner is -automaticallyoperated and responds automatically to the signals transmitted thereto.

References Cited UNITED STATES PATENTS 2,699,381 1/1955 King 18-12,861,294 11/1958 Glaxner et al 18-1 2,917,374 12/1959 Wood 18-13,056,162 10/ 1962 Fisher 18-1 3,142,862 4/1964 Guldman 18-1 3,337,9078/1967 Williams 18-1 WILLIAM I. STEPHENSON, Primary Examiner.

